Unexpected Shower Dents Columbia's Tiles

NASA officials say they do not know if considerable damage to the shuttle Columbia's thermal tiles inflicted by a sudden shower Sunday will delay the craft's Dec. 20 flight.

The damage occurred when a jumbo jet returning Columbia from California to Kennedy Space Center ran into undetected rain that damaged more than 1,000 of the fragile heat-shield tiles.

NASA officials said Thursday that between 200 and 300 tiles probably would have to be replaced.

NASA said in a statement that the 747 jet was flying 253 mph in clear air at 16,000 feet when it ran into light to moderate rain near Montgomery, Ala.

NASA policy forbids launching or flying shuttles through rain.

However, the statement said, ''The shower did not show up on ground radar or the 747's on-board radar system. The air crew reported being in the rain for approximately 20 to 25 seconds. The damaged areas are around the windows and on the forward facing tiles on Columbia.''

A plane flew ahead of the 747 but it didn't detect the shower either. It was too late for the jumbo jet to avoid the rain.

KSC spokesman George Diller said technicians will begin to assess the damage today after Columbia is moved from the Vehicle Assembly Building to the shuttle hangar.

Columbia was being returned from the Rockwell International plant in Palmdale, Calif., where it underwent an 18-month overhaul.

The flagship of the shuttle fleet, Columbia is covered by 33,000 tiles.

The tiles are designed to protect against heat, not the bullet-like impact of raindrops encountered at high speeds.

Columbia, which has flown six missions, is to deploy two satellites on its Dec. 20 mission.